I have a 99 Seville STS with 149,000 miles. No history codes and no current codes. I'm getting 15-20 misfires on #8 cylinder every startup. I switched #8 spark plug, wire and coil with #6 plug, wire and coil. Still misfires on #8 cylinder. Switched them back. Eliminated those 3 things. Switched ignition module with friend's 2000 STS. Still misfires #8 cylinder. Eliminated that. Installed new fuel injector on #8 cylinder. Still misfires on #8. Performed compression test on #2, #4, #6 and #8 cylinders. All were in the same range. I've ran out of ideas! Any suggestions would be appreciated.
1999 STS-Misfire
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Swapped ICMs ??? A 2000 or later ICM bears no resemblance to a 1999 or earlier. Entirely different ignition systems. Entirely. *Unless you are outside the U.S. and the "2000" actually has a build date of between 07/98 and 06/99. THEN it's a 1999 car.
Here's a 2000 and later coil cassette with ICM. Your 1999 should have 4 coils mounted on the right (rear) cam cover.
Have you checked the ICM ground wire - and are the coils properly connected to their respective spark plugs ?
EDIT: *Texas was in the U.S. last time I looked ................
Here's a 2000 and later coil cassette with ICM. Your 1999 should have 4 coils mounted on the right (rear) cam cover.
Have you checked the ICM ground wire - and are the coils properly connected to their respective spark plugs ?
EDIT: *Texas was in the U.S. last time I looked ................
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My friend has salvage yard. He said it came off of a 2000. He was definitely wrong because the one he brought me was identical to mine. In fact, I left it on mine.
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I don't see a ground wire on ICM. Just 2 wire harnesses on each end. Doesn't it ground itself on metal base it's bolted to? The coils are properly connected to their respective spark plugs.
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I don't see a ground wire on ICM. Just 2 wire harnesses on each end. Doesn't it ground itself on metal base it's bolted to? The coils are properly connected to their respective spark plugs.
The ICM grounds to the aluminum plate it is mounted to however that aluminum plate has a ground wire runs behind the engine. It is commonly left off as its a bitch to see. So technically the ICM does have a ground wire. It can cause some issues if left off, it's a heavy gauge wire with a ring terminal on the ends.
Yep ................ That small ground icon on the left end of the ICM is actually the wire/terminals from the plate to the engine.
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The Cam cover doesn't provide a ground. My 97 has the ground on the opposite side right where you can see if and not forget it. I left it off my 98 once during plug change and it ran weird, it ran just not quite right.
This ground wire and the problems associated with it has been discussed in the Engines and Tech Tips forums for years. The OEM wire - black with ring terminals - went from the ICM base over to a bolt near the P/S pump.
EDIT: I've disconnected a few when prowling the junkyards with the car club. The pre-2000 waste spark system is a good swap-in for some older engines and it adapts well to external crank trigger wheels. One reason why the systems, as well as coils, are becoming a bit scarce in junkyards.
EDIT: I've disconnected a few when prowling the junkyards with the car club. The pre-2000 waste spark system is a good swap-in for some older engines and it adapts well to external crank trigger wheels. One reason why the systems, as well as coils, are becoming a bit scarce in junkyards.
Here you go - from the Tech Tips, way back. Eighth and ninth pictures, the large black wire with red shrink tubing on the terminal.
Iametarq refers to it as "looks like a positive terminal".
http://www.cadillacforums.com/forum...981-how-spark-plug-wire-replacement-98-a.html
Iametarq refers to it as "looks like a positive terminal".
http://www.cadillacforums.com/forum...981-how-spark-plug-wire-replacement-98-a.html
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